1. Field of the Invention
The present invention relates to a two-armed transfer robot useful for semi-conductor manufacturing equipment, liquid crystal display processing equipment and the like. More particularly, the present invention relates to a two-armed transfer robot for transferring workpieces between processing chambers under a vacuum.
2. Description of the Related Art
In general, transfer robots are used for semi-conductor manufacturing equipment, liquid crystal display processing equipment and the like. The robot has at least one arm mechanism provided with a handling member. An object to be processed or workpiece such as a silicon wafer is placed on the handling member. The arm mechanism is capable of moving horizontally in a straight line as well as rotating in a horizontal plane. A plurality of processing chambers for performing various kinds of processing are arranged around a rotation axis of the robot. With the use of the transfer robot, the workpiece is suitably brought to and taken away from a selected one of the processing chambers.
For improving efficiency in the transferring operation, use has been made of the so-called two-armed transfer robot having two arm mechanisms. Each arm mechanism has a free end at which a handling member is mounted.
A conventional two-armed transfer robot is disclosed in Japanese Patent Application Laid-open No. 7(1995)-142552 for example.
Referring to FIGS. 14-17 of the accompanying drawings, the prior art robot includes a stationary base frame 80, an inner frame 81 and a first arm 82. The inner frame is rotatable about a vertical axis O1, relative to the base frame 80, while the first arm is rotatable about a first axis P1 extending in parallel to the axis O1. The rotation of the inner frame 81 is actuated by a driving device fixed to the base frame, while the rotation of the first arm 82 is actuated by a driving device fixed to the inner frame 81.
Reference numeral 83 indicates a second arm which is rotatable relative to the first arm 82 about a second axis Q1, extending in parallel to the first axis P1, while reference numeral 84A indicates a handling member which is rotatable relative to the arm 83 about a third axis R1 extending in parallel to the second axis Q1. Reference numeral 85 indicates a first rotation-transmitting member which is fixed to the inner frame 81 coaxially with the first axis P1, while reference numeral 86 indicates a second rotation-transmitting member which is fixed to the second arm 83 coaxially with the second axis Q1.
Reference numeral 87 indicates a third rotation-transmitting member fixed to the first arm 82 coaxially with the second axis Q1, while reference numeral 88 indicates a fourth rotation-transmitting member fixed to the handling member 84 coaxially with the third axis R1.
A first connecting member 89 is provided between the first rotation-transmitting member 85 and the second rotation-transmitting member 86, while a second connecting member 90 is provided between the third rotation-transmitting member 87 and the fourth rotation-transmitting member 88. The distance S between the first and second axes is equal to the distance between the third and fourth axes. The radius ratio of the first rotation-transmitting member 85 to the second rotation-transmitting member 86 is 2 to 1. The radius ratio of the fourth rotation-transmitting member 88 to the third rotation-transmitting member 87 is also 2 to 1.
Chain sprockets or pulleys may be used for the first to fourth rotation-transmitting members 85-88. Correspondingly, the first and second connecting members 89, 90 may be chains or timing belts.
The first arm mechanism 91 is made up of the above-mentioned elements 82-90. A second arm mechanism 92, which is symmetrical to the first arm mechanism with respect to the Xxe2x80x94X line, is supported for rotation about the second axis P2 extending in parallel to the axis O1.
Thus, the distance between the axis O1, and the first axis P1 is equal to that between the axis O1 and the second axis P2. The two-armed transfer robot is made up of the above elements 80-92.
The operations of the first and the second arm mechanisms 91, 92 are symmetrical with respect to the Xxe2x80x94X line and substantially the same. Therefore, description will be made to the operation of the first arm mechanism 91.
First, it is assumed that the inner frame 81 is kept stationary to the fixed base frame 80, and that the first, second and third axes P1, Q1, R1 are initially located on a common straight line, as shown in FIG. 16. Starting from this state, the first arm 82 is rotated counterclockwise through an angle xcex8 about the first axis P1.
During the above operation, the first rotation-transmitting member 85 is stationary, while the second axis Q1 is rotated counterclockwise through the angle xcex8 to be brought to the Q11 position. As a result, a Y1-side portion of the first connecting member 89 is wound around the first rotation-transmitting member 85, whereas a Y2-side portion is unwound from the first rotation-transmitting member 85.
Thus, the first connecting member 89 is shifted in a direction shown by arrows a1 and a2. As a result, the second rotation-transmitting member 86 is rotated clockwise about the second axis Q1.
As previously mentioned, the radius ratio of the first rotation-transmitting member 85 to the second rotation-transmitting member 86 is 2 to 1. Thus, when the first arm 82 is rotated counterclockwise about the first axis P1 through the angle xcex8, the second rotation-transmitting member 86 is rotated clockwise about the second axis Q11 through an angle 2xcex8.
At this time, since the second rotation-transmitting member 86 is fixed to the second arm 83, the second rotation-transmitting member 86 and the second arm 83 are rotated clockwise about the second axis Q1 through an angle 2xcex8.
If the second arm 83 is not moved relative to the first arm 82, the third axis is brought to the R11 position shown by broken lines when the first arm 82 is rotated counterclockwise about the first axis P1 through an angle xcex8, starting from the initial state where the first, the second and the third axes P1, Q1, R1 are positioned on the same line. Actually, however, the second rotation-transmitting member 86 is rotated clockwise about the second axis Q11 through an angle 2xcex8. Therefore, the third axis R11 is rotated clockwise about the second axis Q11 through the angle 2xcex8, and brought to the R12 position.
As a result, after the first arm 82 is rotated counterclockwise about the first axis P1 through an angle xcex8, the third axis R12 is still on the straight line extending through the first and the third axis P1 and R1.
Further, when the second arm 83 is rotated clockwise about the second axis Q11 through an angle 2xcex8 so that the third axis is brought to the R12 position, a Y2-side portion of the second connecting member 90 is wound around the third rotation-transmitting member 87, whereas a Y1-side portion is unwound from the third rotation-transmitting member 87.
As a result, the second connecting member 90 is shifted in a direction b1-b2 shown in FIG. 16. Thus, the fourth rotation-transmitting member 88 is rotated counterclockwise about the third axis R12.
When the second arm 83 is rotated clockwise about the second axis Q11 through an angle 2xcex8 as described above, the fourth rotation-transmitting member 88 is rotated counterclockwise about the third axis R12 through an angle xcex8 since the radius ratio of the fourth rotation-transmitting member 88 to the third rotation-transmitting member 87 is 2 to 1. As a result, a point Co of the fourth rotation-transmitting member 88 is brought to a point C1 on the straight line passing through the first and the third axes P1, R12.
Upon rotation of the first arm 82 about the first axis P1 in the counterclockwise direction as described above, the first arm mechanism 91 is actuated in the X-direction. Accordingly, the handling member 84A is moved along the line passing through the first and the third axes P1, R1. During this movement, however, the handling member 84A does not changed its attitude or orientation since it is fixed to the fourth rotation-transmitting member 88.
Likewise, the second arm mechanism 92 is actuated in the X-direction, while the second handling member 84B keeping its initial attitude along the line passing through the first and the third axes P2, R2.
The first and the second handling members 84A, 84B are arranged between the axes P1, P2 as viewed in the Y1-Y2 direction.
Further, the extremities of the handling members 84A, 84B are vertically spaced from each other. Thus, upon actuation of the arm mechanisms 91, 92, the handling members 84A, 84B can move along the Xxe2x80x94X line passing through the axis O1 without interfering with each other.
When the inner frame 81 is rotated about the axis O1, the first and the second arm mechanisms 91, 92 are simultaneously rotated about the axis O1.
As shown in FIG. 17, a suitable number (six in the figure) of processing chambers are arranged around the axis O1 of the two-armed transfer robot. Workpieces are transferred by the robot to these chambers to be processed.
The prior art transfer robot has been found to have the following disadvantages. First, the fourth rotation-transmitting member 88 and the second connecting member 90 are provided at the extremity of the second arm 83 for maintaining the initial orientation of the handling member 84 along the P1-R1 line. Therefore, the height H1 (see FIG. 15) of the arm mechanism is made unfavorably large. This requires that each processing chamber have a large insertion window to allow the passage of the arm mechanism.
Further, as shown in FIGS. 14-16, the axis P1 of the first arm mechanism 91 and the axis P2 of the second arm mechanism 92 are spaced from each other, with the axis O1 of the inner frame 81 located therebetween. This arrangement renders the rotation radius of the inner frame 81 unfavorably large.
Accordingly, the bearings 93 provided around the inner frame 81 have an unfavorably large diameter, and the magnetic fluid seal 94 for hermetic sealing suffers the same problem. With the use of such bearings and magnetic fluid seal, the overall size of the robot is also increased. Therefore, the price of the robot is rendered unduly high.
Further, the driving devices for linearly moving the handling members 84A, 84B are mounted on the inner frame 81. Thus, the driving devices are rotated together with the inner frame 81. For supplying the driving devices with electricity, use is made of a cable extending from the base frame 80. Thus, the rotation angle or the number of rotation of the inner frame 81 is limited for preventing the cable from breaking.
For realizing the above-mentioned prevention, a suitable monitoring device and a controlling unit are needed to stop the rotation of the inner frame 81 before the rotation angle of the frame exceeds a predetermined threshold value (540xc2x0 for example). However, such additional devices make the robot expensive. More importantly, the additional devices do not eliminate the limitation to the rotation angle. Thus, the conventional robot is not only expensive but inconvenient to operate.
It is, therefore, an object of the present invention to provide a compact, inexpensive two-armed transfer robot which is easy to operate and capable of providing good productivity.
According to a first aspect of the present invention, there is provided a two-armed transfer robot including: a first double-pantograph mechanism and a second double-pantograph mechanism symmetrical to the first double-pantograph mechanism with respect to a vertical plane. Each double-pantograph mechanism includes a first pantograph assembly and a second pantograph assembly. The first pantograph assembly has an inner link, a pair of first intermediate links and an outer link associated with the inner link via the first intermediate links. The second pantograph assembly includes the outer link in common with the first pantograph assembly, a pair of second intermediate links and a hand-supporting link associated with the outer link via the second intermediate links. The inner link is common to the first and the second double-pantograph mechanisms. The robot further includes: rotation-transmitting mechanisms provided between the first and the second intermediate links of the respective double-pantograph mechanism; first and second handling members supported by the hand-supporting links of the first and the second double-pantograph mechanisms, respectively; a stationary base member; first to third shafts coaxially rotatable about a first axis extending vertically; and first to third driving devices for actuating the first to the third shafts, respectively. The driving devices are fixed to the base member.
One of the first intermediate links of the first double-pantograph mechanism is fixed to the first shaft for rotation about the first axis, while one of the first intermediate links of the second double-pantograph mechanism is fixed to the second shaft for rotation about the first axis. The inner link is fixed to the third shaft for rotation about the first axis. The other first intermediate links of the respective double-pantograph mechanisms are supported by the inner link for rotation about a common second axis. The first intermediate links and second intermediate links of each double-pantograph mechanism are equal in length. The second pantograph assembly of each double-pantograph mechanism is offset away from the first axis with respect to the first pantograph assembly of said each double-pantograph mechanism. The first and the second handling members are vertically spaced from each other. The handling members are arranged not only to linearly move in horizontal lines passing through the first axis but to rotate simultaneously around the first axis.
With such an arrangement, the first to the third shafts are coaxially supported about a common vertical axis. Thus, the bearings and the seals provided around the respective shafts are made small in diameter. As a result, the overall size of the transfer robot is rendered relatively small as compared with the conventional robot. Accordingly, the price of the robot is reduced.
Further, according to the present invention, the pantograph assembly carrying a handling member is made advantageously small in thickness since there is no need to use the conventional rotation-transmitting member and connecting member described above Thus, the height H2 of the base portions of the respective handling members is reduced. Accordingly, the size of the insertion window or each processing chamber is also reduced.
Further, the first to the third driving devices are attached to the stationary base member. Therefore, unlike the conventional robot, there is no limitation to the rotational angle of the first and the second handling members around the first axis. Thus, the present invention serves to increase productivity.
The second intermediate links of the respective double-pantograph mechanisms may be arranged in a common plane.
The hand-supporting link of one double-pantograph mechanism may be attached to an upper surface of each second intermediate link of said one double-pantograph mechanism, while the hand-supporting link of the other double-pantograph mechanism may be attached to a lower surface of each second intermediate link of said other double-pantograph mechanism.
The first double-pantograph mechanism may include a third handling member which is attached to the hand-supporting link of the first double-pantograph mechanism in a manner that the third handling member projects opposite to the first handling member. Similarly, the second double-pantograph mechanism may include a fourth handling member which is attached to the hand-supporting link of the second double-pantograph mechanism in a manner that the fourth handling member projects opposite to the second handling member.
Each of the first to the third shafts may be rotatably supported via a magnetic fluid seal for hermetic sealing.
Other objects, features and advantages of the present invention will be fully understood from the following detailed description given with reference to the accompanying drawings.